1. Field of the Invention
The present invention relates to a carriage assembly of a hard disk drive which is provided with a wiring circuit electrically connected to a magnetic head and includes a long tail suspension circuit board where part of the wiring circuit is formed as flying leads and a flexible printed circuit board on which bonding terminals to which the flying leads are bonded are provided.
2. Related Art
In recent years, in the field of hard disk drives (magnetic disk apparatuses), as the recording density of magnetic disks has increased and access speeds have become faster, the construction of a carriage assembly, and in particular the constructions of the suspension and flexible printed circuit board have been rationalized.
More specifically, “suspension circuit boards”, where a wiring circuit is formed in advance on the surface or another part of the suspension that supports a magnetic head, are becoming more common. In addition, to improve the bonding reliability by reducing the number of electrical bonds, it is increasingly common to use a so-called “long tail suspension circuit board” where the suspension circuit board extends as far as the flexible printed circuit board for a preamp provided on the carriage assembly and to directly bond the wiring circuit of the suspension circuit board and the flexible printed circuit board for the preamp to one another without a trunk cable or the like in between.
FIG. 9 is a side elevation of a carriage assembly Cx in which the long tail suspension circuit board described above is used.
A carriage main body 10 of the carriage assembly Cx includes a plurality of carriage arms 10a that extend corresponding to recording surfaces of a plurality of magnetic disks (not shown) that are disposed in parallel. Seek operations within planes that are parallel with the surfaces of the magnetic disks are carried out by rotating the carriage main body 10 by rotating an actuator shaft that has a rotational axis on the line A-A in FIG. 9.
Long tail suspension circuit boards 12 are formed as thin stainless steel plates, are disposed inside channels 10b formed along the extending direction of the carriage arms 10a, and are attached to the carriage main body 10. End parts 12a of the long tail suspension circuit boards 12 protrude from and beyond ends of the carriage arms 10a, and magnetic heads 14 are mounted on surfaces of the end parts 12a that face the magnetic disks.
A flexible printed circuit board 16 for a preamp is attached to a reinforced part on one side surface of the carriage main body 10. The flexible printed circuit board 16 is attached to the reinforced part of the carriage main body 10 by an adhesive applied to the reinforced part and a screw 18.
FIG. 8A is a plan view of a long tail suspension circuit board 12.
A wiring circuit 15 electrically connected to a magnetic head 14 is provided on one surface of the long tail suspension circuit board 12. The wiring circuit 15 is provided from a front end 12a, on which the magnetic head 14 is mounted, to the other end on the carriage main body 10 side and is provided along the length of the long tail suspension circuit board 12.
The wiring circuit 15 is normally provided with two signal lines for writes onto a magnetic disk by the magnetic head 14 and two signal lines for reads, making a total of four signal lines.
The front and rear surfaces of the wiring circuit 15 (i.e., a surface facing the thin stainless steel plate described above and an outer surface) are insulated by being covered with an insulating film, such as a polyimide film.
However, at the other end of the long tail suspension circuit board 12, the wiring circuit 15 is formed of flying leads 15a (parts shaded black in FIG. 8B) that are completely exposed from the thin stainless steel plate described above and the insulating film (see FIG. 3 of Japanese Laid-Open Patent Publication No. 2003-31915).
The flying leads 15a are bonding terminals on the long tail suspension circuit board 12 for bonding to bonding terminals 16a of the flexible printed circuit board 16 for the preamp.
FIG. 10 is an enlargement of bonded parts of the bonding terminals 16a and the flying leads 15a. 
In order to make the direction in which the respective flying leads 15a are aligned parallel with the printed circuit surface of the flexible printed circuit board 16, a part 12b at the other end of the long tail suspension circuit board 12 is bent at a right angle at the line B-B in FIG. 8B so that the formation surface of the wiring circuit 15 is on the inside, with the flying leads 15a being bonded to the bonding terminals 16a. 
The flying leads 15a and the bonding terminals 16a are bonded together by ultrasonic bonding. FIGS. 11A and 11B are cross-sectional views in a direction perpendicular to the direction in which the flying leads 15a extend and show the ultrasonic bonding method.
As shown in FIG. 11A, the flexible printed circuit board 16 is attached on the reinforced part 10c of the carriage main body 10 via an adhesive layer 20. The flying leads 15a of a long tail suspension circuit board 12 are disposed on the bonding terminals 16a of the flexible printed circuit board 16. Next, as shown in FIG. 11B, an ultrasonic tool T is placed in contact with the flying leads 15a and the flying leads 15a are pressed onto the bonding terminals 16a by the ultrasonic tool T. In this state, by applying ultrasonic vibration to the flying leads 15a using the ultrasonic tool T, the flying leads 15a and the bonding terminals 16a are bonded together.
It should be noted that by subjecting the outer surfaces of the flying leads 15a and the bonding terminals 16a to metal plating in advance (see FIG. 3 and Paragraphs 0025 and 0026 of Japanese Laid-Open Patent Publication No. 2003-31915), it is possible to favorably carry out bonding by applying ultrasonic vibration.
In addition, after the ultrasonic bonding, the surfaces of the flying leads 15a that contact the ultrasonic tool T (the upper surfaces of the flying leads 15a in FIG. 11B) become rough due to friction between the surfaces and the ultrasonic tool T, so that it is easy for dust to be produced. Dust present inside a hard disk drive can cause the hard disk drive to malfunction, so that after the ultrasonic bonding, to prevent the production of dust, as shown in FIG. 12, a resin coating 22 that spans the bonding terminals 16a is applied onto the contact surfaces of the flying leads 15a. 
Patent Document 1
Japanese Laid-Open Patent Publication No. 2003-31915 (FIG. 3, and Paragraphs 0025 and 0026).
In the conventional carriage assembly Cx, the flexible printed circuit board 16 and the reinforced part 10c of the carriage main body 10 are attached via the adhesive layer 20, so that as shown in FIGS. 11A and 11B, the thickness of the adhesive layer 20 is not uniform. This means that the pressing force of the ultrasonic tool T does not act uniformly on the plurality (in this example, four) flying leads 15a and the bonding terminals 16a, and therefore the transmission of the ultrasonic vibration is also not uniform, resulting in the problem of fluctuations occurring in the electrical bonding strength between the flying leads 15a and the bonding terminals 16a. 
Also, during the manufacturing process for a hard disk drive, when a fault is discovered in a test of electrical characteristics and the like of the magnetic heads 14 and the long tail suspension circuit board 12 after the assembly of the carriage assembly Cx, in some cases a replacement process for the long tail suspension circuit board 12 becomes necessary.
In this case, it is necessary to pull the flying leads 15a off the bonding terminals 16a, but as shown in FIG. 12, if the resin coating 22 that spans the bonding terminals 16a is applied onto the contact surfaces of the flying leads 15a, it will be necessary to apply, to the flying leads 15a, not only enough force to pull the flying leads 15a off the bonding terminals 16a but also enough force to pull the resin coating 22 off the bonding terminals 16a. This means that there are cases where the application of a large force to the flying leads 15a causes the flying leads 15a to break, resulting in the problem that replacement becomes no longer possible or the replacement process becomes difficult.